Electrolytic method of converting polychloromethyl groups of organic compounds into monochloromethyl groups



United States Patent Oflice 3 425 919 ELECTROLYTIC MIiTHbD OF CONVERTING POLYCHLOROMETHY L GROUPS OF ORGANIC COMPOUNDS INTO MONOCHLOROMETHYL GROUPS Masanori Nagao, Kanagawa-ken, Naotake Sato,

and Takekazu Akashi, Kanagawa-ken, to Ajinomoto 'Co., Inc., Tokyo, Japan No Drawing. Filed Mar. 10, 1966, Ser. No. 533,221 Claims priority, application Japan, Mar. 13, 1965, 40/ 14,491; May 1, 1965, 40/25,526 US. Cl. 204-73 Int. Cl. B01k 1/00 wherein n is 2 or 3, and R is an aliphatic radical having a carbon chain of at least two carbon atoms can be reduced cathodically with excellent yields in an electrolyte which contains a halide of an alkali metal, ammonium, or alkaline earth metal, or a salt of a mineral acid or organic sulfonic acid with a lower-alkylamine or with quaternary lower-alkylammonium.

The nature of the radical R in the above formula is not in itself critical, when the dior trichloromethyl group is the terminal member of the carbon chain. When R is the radical of a saturated or unsaturated aliphatic hydrocarbon, it remains unaffected by the electrolysis. Functional substituents which are found unaltered in the ultimate product include halide, cyano, hydroxyl, carboxyl and carboalkoxyl. Substituents which are reduced at the cathode do not prevent the conversion of a simultaneously present dichloromethyl group or trichloromethyl group to the monochloromethyl group.

The various'monochloromethyl derivatives of aliphatic compounds available by the method of the invention are useful intermediates because of the ease with which the single chlorine atom is replaced by other substituents in a well known manner to form amines, carboxylic acids, alcohols, and other compounds. The chlorine removed from the starting material may be recovered in the gaseous state from the anode of the electrolytic cell in which the dechlorination reaction is carried out.

The cell is preferably employed with a diaphragm or other means for preventing mixing of the catholyte and the anolyte. The composition of the anolyte is not directly relevant to the success of the method. The composition of the catholyte is at the core of this invention.

The catholyte is a solution of the compound to be dechlorinated and of an ionizable salt in a homogeneous, single-phase, liquid mixture of water and of an organic solvent selected to dissolve both the salt and the starting compound. The salt and the solvent must be stable at the cathode if contamination of the desired product is to be avoided.

The salts which have been found suitable for the method of the invention include the halides of the alkali metals, of ammonium and of the alkaline earth metals. Lithium and ammonium are the preferred cations of this group of salts, but the others are also operative. The chlorides are preferred because of their ready availability and are generally lower cost, particularly in view of the ab- Tokyo, Japan, assignors 5 Claims 3,425,919 Patented Feb. 4, 1969 sence of any known advantages of using bromides, iodides or fluorides.

Other salts which have been used successfully for providing the catholyte with adequate conductivity include the salts of lower-alkylamines or of quaternary loweralkylammonium with mineral acids or strong organic sulfonic acids. Hydrochloric, sulfuric and nitric acid, which are the most common mineral acids, and benzenesulfonic acid and toluenesulfonic acid, the sulfonic acids most readily available, are preferred as the acid moieties of the salts in the absence of advantages to be gained from the more costly acids of the same types. The salts of hydrochloric, sulfuric and toluenesulfonic acid have been found to combine the most desirable features.

Salts of primary, secondary and tertiary amines, and of quaternary ammonium with these acids may be employed. The alkyl radicals of these amine or ammonium salts may have 1 to 6 carbon atoms, and may be further substituted. The benzylamine and benzylammoniumfsalts are typical of such salts having substituted alkyl radicals. The amount of ionizing salt employed is not critical, and will normally be between two and 'five moles per mole of the polychloromethyl compound to be treated.

The organic solvent employed must be at least somewhat soluble in water and capable of dissolving the polychloromethyl compound in the presence of water. It should preferably be unaffected by the conditions prevailing at the cathode during current passage. The lower alkanols and the lower-alkylcellosolves are readily available solvents which meet these requirements.

Conventional methods and conventional equipment may be used in preparing the catholyte but it is often simplest to dissolve the polychloromethyl compound in the organic solvent, to dissolve the ionizing salt separately in the water, and then to combine the aqueous and organic solutions.

The material of the electrodes may be selected according to the rules common to this art. The cathode may be made of copper, lead, cadmium, zinc, mercury, aluminum, tin or other metals unaffected by the catholyte, whereas the anode has to resist chlorine or is to be made of material whose consumption by chlorine is economically bearable.

An anolyte which does not make the catholyte inoperative when accidentally admixed thereto is preferred. The anolyte, therefore, preferably is an aqueous solution of one of the ionizable salts referred to above.

The current density at the cathode or anode is not critical, and the method is operative at all temperatures at which the electrolyte is in the liquid state. The current efliciency is affected to some degree by such process variables as temperatures, current density and concentration of the other constituents in the solvent of the electrolyte, and optimum variables have to be determined experimentally for a given set of fixed conditions if high est current efficiency is to be achieved. The cost of electric current, however, is not usually an important factor in performing the method of the invention.

The cathode current efiiciency is generally a direct function of the concentration of polychloromethyl compound in the catholyte so that the current etficiency decreases as the reaction proceeds. Depending on the degree of conversion desired, the current passed through the cell may be between and 300% of the electrochemical equivalent of the removed chlorine.

If the anode and cathode compartments of the electrolytic cell are separated by a diaphragm during operation, and if the polychloromethyl compound does not contain functional groups which undergo secondary reactions, the desired monochloromethyl compound is readily removed from the spent catholyte by solvent extraction. The recovery methods to be employed in the presence of by-products are readily selected to suit prevailing conditions.

The following examples are further illustrative of the method of the invention but it will be understood that the invention is not limited to the examples.

Example 1 An electrolytic cell having two compartments separated by a porcelain diaphragm was provided with a pool of mercury in one compartment. The mercury, which served as the cathode, weighed one kilogram and had an exposed surface of 50 square centimeters. The cathode compartment was equipped with an external heater and a thermostat,-and with a magnetic stirrer.

The cathode compartment was filled with a catholyte of the following composition:

1,1,1,5-tetrachloropentane g Methanol ml 180 Water ml Tetraethylammonium p-toluenesulfonate g 30 The anode compartment received 30 ml. of an aqueous molar solution of tetraethylammonium p-toluenesulfonate and a platinum electrode having an exposed surface of 50 square centimeters in the anolyte.

A current of 2.0 amps. was passed through the cell for five hours while the catholyte was being agitated and kept at approximately C. The catholyte was then poured into approximately 300 milliliters water, and the resulting mixture was extracted with chloroform. The extract was washed with water, dried over desiccated sodium sulfate, and evaporated in a vacuum.

The residue consisted of 6.0 g. 1,5-dichloropentane boiling at 7980 C. at 21 mm. Hg, and was free of tetrachloropentane. The yield was 90%, the cathode current efficiency somewhat less than 50%.

Example 2 A catholyte prepared from 1,1-dichloropentene-3-ol-5 g 10.0 Methanol ml 180.0 Water ml 20.0 Tetramethylammonium nitrate g 27.2

was electrolyzed for four hours in the apparatus of Example 1 under otherwise identical conditions and was worked up as described above.

There were obtained 6.6 g. 1-chloropentene-3-ol-5 of RP. 80 C. at 6 mm. Hg (85% yield).

Example 3 The mercury cathode of the cell described in Example 1 was replaced by a lead plate of equal effective surface area, and the cathode compartment was charged with a solution of 1,1,7-trichloroheptane g 11.6 Methylcellosolve ml 200 Water ml- 25 Tetraethylammonium chloride g 15 The anode and anolyte were as described in Example 1. A current of 2.0 amps. was passed through the cell at a catholyte temperature of about 25 C. with agitation for 2.5 hours.

The catholyte was then poured into about 800 milliliters water, and the mixture was extracted with chloroform. The washed and dried extract was evaporated in a vacuum to remove the solvent, and 3.2 g. 1,7-dichloroheptane (B.P. 76-78 C. at 1.5 mm. Hg) and 6.0 g. unreacted 1,1, 7-trichloroheptane were recovered from the residue by fractionation. The yield, based on the consumed trichloroheptane, was 69%.

4 Example 4 The cell described in Example 1 was charged with a catholyte of 1,1,5-trichloropentane g 10 Methanol ml 180 Water ml 20 Tetramethylammonium bromide g 40 The anolyte consisted of 30 ml. aqueous, molar tetramethylarnmonium nitrate solution. A current of 2.0 amps. was passed through the cell for 2.5 hours at a temperature of 25 C.

The catholyte was worked up as in Example 1, and 6.8 g. 1,5-dichloropentane (B.P. -101 C. at 56 mm. Hg) were recovered for a yield of 85%.

Example 5 The procedure of Example 1 was repeated with 10 grams 1,1,1,5-tetrachloropentane, but the electrolysis was carried out for 3.5 hours only. The product recovered consisted of 5.4 g. 1,5-dichloropentane (B.P. 101-102 C. at 58 mm. Hg). The yield was 81%.

Example 6 The mercury cathode of the cell described in Example 1 was replaced by a cadmium plate of the same effective.

surface area, and the cell was charged with a catholyte of the following composition:

1,1-dichloropentane g 14 Ethanol ml 180 Water ..*ml.. 20 Ammonium chloride g 12 The anolyte consisted of 30 ml. of an aqueous molar lithium nitrate solution. A current of 2 amps. was passed through the cell at 25 C. for 3 hours. The catholyte was worked up as in Example 1, and 3.3 g. l-chloropentane (B.P. -106 C.) and 7.7 g. of unreacted dichloropentane were recovered. The yield, based on the consumed and the anolyte of Example 1 were electrolyzed in the apparatus described in Example 1 at 2.0 amps. for four hours.

When the catholyte was worked up .as in Example 1, 6.3 g. 6-chlorocapronitrile (B.P. 122-123 C. at 15 mm. Hg) were obtained (95% yield).

Example 8 The procedure of Example 7 was repeated with a catholyte consisting of 5,5,5-trichloropentanol-1 g 10.0 Methanol ml Water ml 20 Tetramethylammonium chloride g 22 5-ch1oropentanol-1 (B.P. 90-93 C. at 17 mm. Hg) was recovered from the catholyte in a yield of 92% (5.9 g.).

Example 9 The procedure of Example 1, when applied to a catholyte consisting of 5,5,5-trichlorovaleric acid g 10 Methanol ml 180 Water ml 20 Dimethylamine hydrochloride g 16.3

yielded 5.3 g. (80%) S-chlorovaleric acid (B.P. 99-102 C. at 2 mm. Hg).

Example Substitution of trichloroamyl acetate for the trichlorovaleric acid of Example 9 produced 6.4 g. (90%) 5-chloroamyl acetate (B.P. 82-84 C. at 2 mm. Hg).

Example 11 The cell described in Example 1 was charged with a catholyte consisting of The anolyte used was a molar solution of lithium nitrate in water. A current of 2.0 amps. was passed through the cell at 35 C. for 3.5 hours.

3.1 g. 1,5-dichloropentane (B.P. 9698 C. at 53 mm. Hg) and unreacted trichloropentane were recovered when the catholyte was worked up as described in Example 1.

under otherwise identical conditions. 1-ch10ro-5-cyan0- pentene-3 was recovered from the catholyte in a yield of 6.1 g. (94%). None of the starting material was found after electrolysis.

Example 13 The cell described in Example 1 was operated with the same .anolyte and with a catholyte consisting of 5,5,5-trichloropentane-2-ol-l g 10 Methanol ml 180 Water .ml 20 Trimethylamine hydrochloride g 19.1

A current of 2.0 amps. was passed through the cell at 25 C. for 3.5 hours. The catholyte was worked up as in Example 1. None of the starting material was found, and 6.0 g. S-chloropentene-Z-ol-l (B.P. 80 C. at 6 mm. Hg) were recovered (93% yield).

Other compounds which have been successfully dechlorinated by the method illustrated in the preceding examples include 1,1,1-trichloropentane; 1,1,1-trichloroheptane; 1,1,1,3-tetrachloropropane; 1,1,1-trichloro-4-hydroxybutane; 1,1,1-trichloro-S-cyanopentane; 1,1,1,7-tetrachloroheptane;

6 1,1,1,5-tetrachloropentane-3; l, l,1-trichloro-S-hydroxypentene-3 While the invention has been described with reference to specific embodiments, it is to be understood that it is not limited to the examples chosen for illustration but is to be construed broadly and limited solely by the spirit and scope of the appended claims.

What we claim is:

1. An electrolytic method of converting a polychloromethyl group of an organic compound of the formula Ol H CR into the corresponding monochloromethyl group which comprises (a) dissolving said compound and an ionizable salt in a mixture of water and an organic solvent soluble in said water; and

(b) passing electric current between a cathode in contact with the solution so obtained and said solution until said polychloromethy-l group is converted to said monochloromethyl group.

(1) n being 2 or 3, and Rbeing an aliphatic radical having at least two carbon atoms,

(2) said ioniza'ble salt being a member of the group consisting of halides of alkali metal, ammonium and alkaline earth metal, and salts of lower-alkyl .amines, benzylarnines and quaternary lower-alkyl ammonium with a mineral acid or strong organic sulfonic acid.

2. A method as set forth in claim 1, wherein R has two to nine carbon atoms.

3. A method as set forth in claim 1, wherein said carbon atoms of R include a hydrocarbon chain of two to six carbon atoms.

4. A method as set forth in claim 3, wherein said chain is straight, said Cl H C is attached to one of two terminal members of the chain, and the other terminal member has the formula CH -X, X being a member of the group consisting of hydrogen, chlorine, hydroxyl, cyano, carboxyl, and lower-alkylcarboxy.

5. A method as set forth in claim 1, wherein said aliphatic radical has a hydrocarbon chain of at least two carbon atoms, said Cl H C-- being attached to one of the terminal members of said chain.

References Cited UNITED STATES PATENTS 1,627,881 5/ 1927 Bellone 204-73 2,749,293 6/195 6 Wahlin 204-73 FOREIGN PATENTS 848,807 7/ 1952 Germany.

JOHN H. MACK, Primary Examiner. H. M. FLOURNOY, Assistant Examiner. 

1. AN ELECTROLYTIC METHOD OF CONVERTING A POLYCHLOROMETHYL GROUP OF AN ORGANIC COMPOUND OF THE FORMULA 